milek7/sim branch opengl 3.3 renderer import

geometrybank.cpp

@@ -47,6 +47,113 @@ basic_vertex::deserialize( std::istream &s ) {
     texture.y = sn_utils::ld_float32( s );
 }
 
+// based on
+// Lengyel, Eric. “Computing Tangent Space Basis Vectors for an Arbitrary Mesh”.
+// Terathon Software, 2001. http://terathon.com/code/tangent.html
+void calculate_tangent(vertex_array &vertices, int type)
+{
+    size_t vertex_count = vertices.size();
+
+    if (!vertex_count || vertices[0].tangent.w != 0.0f)
+        return;
+
+    size_t triangle_count;
+    if (type == GL_TRIANGLES)
+        triangle_count = vertex_count / 3;
+    else if (type == GL_TRIANGLE_STRIP)
+        triangle_count = vertex_count - 2;
+    else if (type == GL_TRIANGLE_FAN)
+        triangle_count = vertex_count - 2;
+    else
+        return;
+
+    std::vector<glm::vec3> tan(vertex_count * 2);
+
+    for (size_t a = 0; a < triangle_count; a++)
+    {
+        size_t i1, i2, i3;
+        if (type == GL_TRIANGLES)
+        {
+            i1 = a * 3;
+            i2 = a * 3 + 1;
+            i3 = a * 3 + 2;
+        }
+        else if (type == GL_TRIANGLE_STRIP)
+        {
+            if (a % 2 == 0)
+            {
+                i1 = a;
+                i2 = a + 1;
+            }
+            else
+            {
+                i1 = a + 1;
+                i2 = a;
+            }
+            i3 = a + 2;
+        }
+        else if (type == GL_TRIANGLE_FAN)
+        {
+            i1 = 0;
+            i2 = a + 1;
+            i3 = a + 2;
+        }
+
+        const glm::vec3 &v1 = vertices[i1].position;
+        const glm::vec3 &v2 = vertices[i2].position;
+        const glm::vec3 &v3 = vertices[i3].position;
+
+        const glm::vec2 &w1 = vertices[i1].texture;
+        const glm::vec2 &w2 = vertices[i2].texture;
+        const glm::vec2 &w3 = vertices[i3].texture;
+
+        float x1 = v2.x - v1.x;
+        float x2 = v3.x - v1.x;
+        float y1 = v2.y - v1.y;
+        float y2 = v3.y - v1.y;
+        float z1 = v2.z - v1.z;
+        float z2 = v3.z - v1.z;
+
+        float s1 = w2.x - w1.x;
+        float s2 = w3.x - w1.x;
+        float t1 = w2.y - w1.y;
+        float t2 = w3.y - w1.y;
+
+		float ri = (s1 * t2 - s2 * t1);
+		if (ri == 0.0f) {
+			//ErrorLog("Bad model: failed to generate tangent vectors for vertices: " +
+			//         std::to_string(i1) + ", " + std::to_string(i2) + ", " + std::to_string(i3));
+			// useless error, as we don't have name of problematic model here
+			// why does it happen?
+			ri = 1.0f;
+		}
+
+		float r = 1.0f / ri;
+        glm::vec3 sdir((t2 * x1 - t1 * x2) * r, (t2 * y1 - t1 * y2) * r,
+            (t2 * z1 - t1 * z2) * r);
+        glm::vec3 tdir((s1 * x2 - s2 * x1) * r, (s1 * y2 - s2 * y1) * r,
+            (s1 * z2 - s2 * z1) * r);
+
+        tan[i1] += sdir;
+        tan[i2] += sdir;
+        tan[i3] += sdir;
+
+        tan[vertex_count + i1] += tdir;
+        tan[vertex_count + i2] += tdir;
+        tan[vertex_count + i3] += tdir;
+    }
+
+    for (size_t a = 0; a < vertex_count; a++)
+    {
+        const glm::vec3 &n = vertices[a].normal;
+        const glm::vec3 &t = tan[a];
+        const glm::vec3 &t2 = tan[vertex_count + a];
+
+        vertices[a].tangent = glm::vec4(glm::normalize((t - n * glm::dot(n, t))),
+            (glm::dot(glm::cross(n, t), t2) < 0.0F) ? -1.0F : 1.0F);
+    }
+}
+
 // generic geometry bank class, allows storage, update and drawing of geometry chunks
 
 // creates a new geometry chunk of specified type from supplied vertex data. returns: handle to the chunk